1. Field of the Invention
The present invention relates to a cationically polymerizable liquid composition that, without containing an organic solvent, can be coated easily on a substrate and can be polymerized by light or heat after the coating so that it can be used as a pressure-sensitive adhesive having good tack properties. The present invention also relates to a tacky polymer that can be obtained by cationic polymerization of the above-mentioned cationically polymerizable liquid composition.
2. Description of the Related Art
With regard to conventional pressure-sensitive adhesives, a solvent type in which a rubber or acrylic material is dissolved in an organic solvent, and an emulsion type in which the material is dispersed in water have been used. Currently, solvent type pressure-sensitive adhesives are most widely used, but the release of the organic solvent has become an issue recently. The emulsion type has the drawbacks of poor water resistance, long drying time, etc. A hot-melt type, which has been proposed as a method for resolving the above-mentioned problems, still has poor coating performance, poor tack properties and, in particular, poor heat resistance.
Recently, a solvent-free liquid curable pressure-sensitive adhesive has been proposed that is formed mainly from a polymerizable monomer, and a large number of proposals have been made regarding a radically photocurable solvent-free liquid composition employing a radically polymerizable acrylate. However, since it is difficult to complete the radical polymerization in air due to the polymerization inhibiting effect of oxygen, the remaining monomer causes problems such as an unpleasant odor and skin irritation. In order to improve the above-mentioned polymerization, it has been proposed that irradiation with light should be carried out under an atmosphere of nitrogen, but the equipment cost is too high.
A large number of cationically photopolymerizable compositions have been proposed as having good photopolymerization properties in air. For example, JP-A-5-78639 (JP-A denotes Japanese unexamined patent application publication) discloses a pressure-sensitive adhesive comprising a polymer obtained by the copolymerization of acrylic vinyl monomers having a hydroxy group, a bi- or poly-functional epoxy compound, and a cationic polymerization initiator. JP-A-8-60127 discloses a UV curable hot-melt pressure-sensitive adhesive composition comprising a cyclohexene monoepoxide group-containing thermoplastic acrylic polymer, a polyol, and a cationic polymerization photoinitiator. JP-A-11-166168 discloses an acrylic pressure-sensitive adhesive composition comprising an acrylic oligomer obtained by polymerizing specified monomer components, and a cationic photocatalyst. However, since all of these compositions have low polymerizability, a large amount of light is needed when they are cured at room temperature, and the low polymerizability might cause a problem in practice. It is surmised that, since these compositions contain an ester group ascribable to the acrylic group, the presence of the ester group retards the ring-opening polymerization of the cyclic ether, thereby lowering the polymerizability. Furthermore, when the acrylic oligomer has a high molecular weight, the composition becomes highly viscous, thus making it difficult to coat the composition.
In order to avoid the retardation in polymerization due to the ester group, a cationically photopolymerizable composition has been disclosed (Eric-Jack Gerard and Jurgen Schneider, Rad. Tech. Europe 97, 175, 1997), the composition employing a material into which an epoxy group had been incorporated by oxidation of a block polymer having an unsaturated bond in its main chain. JP-A-2000-26830 discloses a UV curable pressure-sensitive adhesive composition formed by mixing a specified epoxy compound, a compound having a functional group that reacts with an epoxy group, a compound having rubber elasticity, and a cationically curing catalyst. However, all of the compositions are very highly viscous; it is proposed in the former that the composition is heated during coating, and in the latter that a solvent is used.
JP-A-11-80681 discloses a foamed pressure-sensitive adhesive tape employing a cationically photoreactive oligomer type pressure-sensitive adhesive composition. Only two types of the composition are disclosed, one of which is the same as that above disclosed by Gerard, et al. and is highly viscous so that it is difficult to coat. The other composition is the same as one disclosed in JP-A-11-166168, and it can be easily expected that its curing speed will be low.
JP-A-11-158437 discloses an adhesion method wherein a pressure-sensitive adhesive material containing a cationically polymerizable compound and a cationic photopolymerization initiator is discharged from a head of an ink-jet printer, coated, and then polymerized by irradiation with light. Although the composition disclosed in the example of the above-mentioned publication has low viscosity, since its polymerizability is low and little polymerization takes place with the level of irradiation described in the publication, it is of no practical utility.
As hereinbefore described, among the solvent-free liquid curable pressure-sensitive adhesives reported so far, there are no reports of a pressure-sensitive adhesive that has ease of coating, can be rapidly polymerized in air and can form a coating of the pressure-sensitive adhesive having good tack properties by irradiation with light.
The present invention has been carried out in view of the above-mentioned circumstances.
It is an object of the present invention to provide a novel cationically polymerizable liquid composition that has ease of coating and high polymerizability in air, and can give a tacky coating having excellent tack properties such as adhesion, holding power, and tack after cationic polymerization. It is another object of the present invention to provide a tacky polymer having excellent tack properties such as adhesion and holding power.
As a result of an intensive investigation by the present inventors in order to achieve ease of coating, high polymerizability in air, and good tack properties after polymerization, the present invention has been accomplished. That is to say, the above-mentioned objects can be realized by a low viscosity cationically polymerizable liquid composition comprising a polymerizable mixture (A) comprising a monofunctional monomer, a polyfunctional monomer and a latent cationic polymerization initiator, the monomers having as a cationically polymerizable group in the molecule a cyclic ether having ring-opening polymerizability; and a solid resin (B) having compatibility with the polymerizable mixture (A). The solid resin (B) here preferably has a softening point of at least 40xc2x0 C. The above-mentioned xe2x80x98low viscosityxe2x80x99 means that the viscosity at 25xc2x0 C. is 20 Paxc2x7sec or below.
One aspect of the present invention relates to a cationically polymerizable liquid composition, which is a liquid resin having a viscosity at 25xc2x0 C. of 20 Paxc2x7sec or below, comprising a cationically polymerizable mixture (A) comprising a monofunctional monomer (A-1) having only one cyclic ether structure represented by formula (1) below in the molecule (hereinafter, also simply called xe2x80x98monofunctional monomerxe2x80x99), a polyfunctional monomer (A-2) having in the molecule at least two groups derived from a cyclic ether structure represented by formula (1) below (hereinafter, also simply called xe2x80x98polyfunctional monomerxe2x80x99), and a latent cationic polymerization initiator (A-3); and a solid resin (B) that is compatible with the above-mentioned mixture (A) at room temperature and has a softening point of at least 40xc2x0 C. 
In the formula, n denotes 0, 1, or 2, and R1 to R6 independently denote hydrogen atoms or hydrocarbon groups, which may have a substituent.
Another aspect of the present invention relates to a tacky polymer that can give excellent tack properties and a polymerizable liquid composition for a tacky polymer, which are obtained by adjusting, so as to be in a specified range, the viscoelastic characteristics of a polymer that is obtained by cationic polymerization of the above-mentioned cationically polymerizable liquid composition.
The above-mentioned objects, other objects, features, and advantages of the invention will become clear from the following description.
The cationically polymerizable liquid composition of the present invention and the tacky polymer obtained by polymerization of the above-mentioned composition are explained in detail below.
Cationically Polymerizable Mixture (A)
A cationically polymerizable mixture (A) contains three essential components. These are a monofunctional monomer (A-1) having in the molecule only one cyclic ether structure having ring-opening polymerizability and represented by the aforementioned formula (1), a polyfunctional monomer (A-2) having in the molecule at least two cyclic ether structures represented by the aforementioned formula (1), and a latent cationic polymerization initiator (A-3). The cationically polymerizable mixture preferably contains a compound having at least two alicyclic epoxy groups as polyfunctional monomer (A-2) in order to further obtain excellent adhesive holding power at high temperature. The xe2x80x98alicyclic epoxy groupsxe2x80x99 will be explained in detail later. It is also preferable to add a compound having a terminal hydroxy group (explained later) as an optional component.
The above-mentioned components of the cationically polymerizable mixture (A) are explained in more detail below.
Monofunctional Monomer (Component A-1)
The monofunctional monomer is a compound having only one cyclic ether structure in the molecule. A compound having at least two cyclic ether structures is classified as a polyfunctional monomer (A-2) below. The monofunctional monomer is used in order to control the viscosity of the polymerizable liquid composition and the glass transition temperature of a polymer that is obtained by polymerizing the composition.
The viscosity of the monofunctional monomer used as the component A-1 is preferably 20 mPaxc2x7sec or below at 25xc2x0 C. However, the viscosity of the monofunctional monomer itself is not particularly limited as long as the liquid composition finally obtained has a viscosity at 25xc2x0 C. of 20 Paxc2x7sec or below.
The monofunctional monomers can be classified roughly into compounds having a three-membered epoxy ring, those having a four-membered oxetanyl ring, those having a five-membered tetrahydrofurfuryl ring, etc., represented by formulae (4) to (6) below. The epoxy group represented by formula (4) includes an alicyclic epoxy group having a structure obtained by epoxidizing a cyclopentene group or a cyclohexene group. 
In formula (4), R1 to R4 independently denote hydrogen atoms or hydrocarbon groups, which may have a substituent, and R1 and R3 may bond to each other to form, together with the carbon atoms to which they are bonded, an alicyclic group (preferably a cyclohexane ring or a cyclopentane ring). The substituents that are introduced into the above-mentioned hydrocarbon groups do not include any of the cyclic ether structures represented by formula (1). This applies also to formulae (5) and (6) below.
With regard to the hydrocarbon groups, alkyl groups or aryl groups having 1 to 36 carbon atoms (these are also described as xe2x80x98C1 to C36xe2x80x99 in the present invention) are preferable, and C1 to C24 alkyl groups or aryl groups are more preferable; with regard to the aryl groups, phenyl groups and naphthyl groups are preferable. With regard to the substituents of the hydrocarbon groups, any substituent is allowed as long as it does not interfere with the cationic polymerization, and a substituent that does not adversely affect the cationic polymerization is preferable.
Examples of the above-mentioned substituents of the alkyl groups include C1 to C12 alkoxy groups, C2 to C12 acyloxy groups, C2 to C12 alkoxycarbonyl groups, phenyl groups, benzyl groups, benzoyl groups, benzoyloxy groups, halogen atoms, cyano groups, nitro groups, phenylthio groups, hydroxy groups and triethoxylsilyl groups.
Examples of the above-mentioned substituents of the aryl groups include C1 to C12 alkyl groups, C2 to C12 alkoxy groups, C2 to C12 acyloxy groups, alkoxycarbonyl groups, phenyl groups, benzyl groups, benzoyl groups, benzoyloxy groups, halogen atoms, cyano groups, nitro groups, phenylthio groups, hydroxy groups and triethoxylsilyl groups. 
In formula (5), R1 to R6 denote hydrogen atoms or hydrocarbon groups, which may have a substituent.
With regard to the hydrocarbon groups, C1 to C36 alkyl groups or aryl groups are preferable, and C1 to C24 alkyl groups or aryl groups are more preferable; with regard to the aryl groups, phenyl groups and naphthyl groups are preferable. With regard to the substituents of the hydrocarbon groups, any substituent is allowed as long as it does not interfere with the cationic polymerization, and a substituent that does not adversely affect the cationic polymerization is preferable. Examples of substituents that are allowed in the hydrocarbon groups are the same as those cited as examples of the substituents of R1 to R4 in formula (4) when R1 to R4 are alkyl groups or aryl groups. 
In formula (6), R1 to R8 denote hydrogen atoms or hydrocarbon groups, which may have a substituent.
With regard to the hydrocarbon groups, C1 to C36 alkyl groups or aryl groups are preferable, and C1 to C24 alkyl groups or aryl groups are more preferable; with regard to the aryl groups, phenyl groups and naphthyl groups are preferable. With regard to the substituents of the hydrocarbon groups, any substituent is allowed as long as it does not interfere with the cationic polymerization, and a substituent that does not adversely affect the cationic polymerization is preferable. Examples of substituents that are allowed in the hydrocarbon groups are the same as those cited as examples of the substituents of R1 to R4 in formula (4) when R1 to R4 are alkyl groups or aryl groups.
Among these monomers, it is preferable in the present invention to use a monofunctional monomer in which any one of R1 to R6 in the above-mentioned formula (1) is a substituent that includes a group represented by formula (2) below. That is to say, a substituent that includes a group represented by formula (2) can be chosen preferably as the hydrocarbon group in formulae (4) to (6). 
In formula (2), R7 and R8 independently denote hydrogen atoms or alkyl groups, which may have a substituent; the number of carbon atoms in the alkyl groups is preferably 1 to 24, and more preferably 1 to 10. R9 is a straight- or branched-chain alkyl group that has at least 4 carbon atoms, and preferably 4 to 24 carbon atoms, and may have a substituent. X denotes xe2x80x94CH2 or, preferably, an oxygen atom.
With regard to a substituent that can be introduced into the alkyl groups represented by R7 to R9, any substituent is allowed as long as it does not interfere with the cationic polymerization, and a substituent that does not adversely affect the cationic polymerization is preferable. Examples of substituents that are allowed in the alkyl groups are the same as those cited as examples of the substituents of R1 to R4 in formula (4) when R1 to R4 are alkyl groups.
In the present invention, the monofunctional monomer (A-1) is particularly preferably a cyclic ether represented by formula (3) below. 
In formula (3), R7, R8 and R10 denote hydrogen atoms or C1 to C10 alkyl groups, which may have a substituent, R9 denotes a straight- or branched-chain C4 to C24 alkyl group, and X denotes an oxygen atom.
It is preferable for R9 to be a C4 to C24 alkyl group, which may have a substituent, or a C6 to C16 straight- or branched-chain alkyl group. Examples of substituents that are allowed in the alkyl group are the same as those cited as examples of the substituents of R1 to R4 in formula (4) when R1 to R4 are alkyl groups.
Specific examples of the compound represented by formula (3) include OXT-212 in which R7=R8=H, R10=ethyl, R9=2-ethylhexyl, and X=oxygen, and OXR-12, which is represented by formula (7) below (manufactured by Toagosei Co., Ltd.). 
Since component A-1 has a comparatively low molecular weight, if there is a large amount of component A-1 remaining in a tacky polymer after polymerization, there is the problem that an unpleasant odor, etc. might occur. Since the use of a monofunctional monomer having an oxetane ring having high cationic polymerizability can control such a problem to a great extent, it is particularly preferable to use a monofunctional monomer of the oxetane type represented by the above-mentioned formulae (3), (5) and (7) as component A-1.
Polyfunctional Monomer (Component A-2)
Component A-2 is a polyfunctional monomer having in the molecule at least two cyclic ether structures, which correspond to the cyclic structure in the above-mentioned formula (1). This component is used in order to adjust the viscosity of the cationically polymerizable liquid composition and the tack properties of the polymer obtained by cationic polymerization, that is to say, the complex modulus of elasticity of the polymer. A connecting group for connecting said at least two cyclic ether structures can be chosen appropriately.
The viscosity of the polyfunctional monomer itself, which is used as component A-2, is not particularly limited as long as the viscosity of the cationically polymerizable liquid composition prepared using the polyfunctional monomer is 20 Paxc2x7sec or below.
It is preferable for the cyclic ether structures of the polyfunctional monomer to be the three-membered epoxy rings, four-membered oxetanyl rings, or five-membered tetrahydrofurfuryl rings that are mentioned above in the explanation of the monofunctional monomer. With regard to specific chemical structures of the cyclic ether groups of the polyfunctional monomer, there can be cited cyclic ether structures obtained by removing one hydrogen atom or any residue from among the hydrogen atoms and hydrocarbon groups connected to the carbon atoms forming the rings in the chemical structures represented by the aforementioned formulae (4) to (6). The polyfunctional monomer having xe2x80x98nxe2x80x99 cyclic ether groups (n denotes an integer of 2 or above) in the molecule has a chemical structure in which such cyclic ether groups are each bonded via a single bond through an n-valent organic residue.
Specific examples of component A-2 include those generally known as epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins, novolac epoxy resins and alicyclic epoxy resins, and EKP-206 and EKP-207 (both trade names; manufactured by Kraton Polymers), which are produced by introducing an epoxy group by oxidizing a block polymer having an unsaturated bond in its main chain, the block polymer being produced commercially by anionic polymerization of an ethylene compound and a diene compound such as butadiene. EKP-206 and EKP-207 are an epoxidized polyisoprene/poly(ethylene/butylene/styrene) and an epoxidized polyisoprene/poly(ethylene/butylene), respectively. The examples further include OXT-121 and OXT-221 (both trade names; manufactured by Toagosei Co., Ltd.), which are oxetane compounds having at least two four-membered cyclic ether oxetanyl groups in their molecules. However, the present invention is not limited by these examples.
An alicyclic epoxy compound used as component A-2 is a component that is effective in maintaining a high complex modulus of elasticity at high temperature. Its viscosity is not particularly limited as long as the viscosity of the composition that is finally obtained is 20 Paxc2x7sec or below.
The alicyclic epoxy compound is a compound having at least two, and preferably 2 to 8, alicyclic epoxy groups in the molecule. An alicyclic epoxy group can be obtained by epoxidizing a cycloolefin. Specific examples of the alicyclic epoxy compound include commercial products such as Epikote 171 (trade name; manufactured by Yuka Shell Epoxy K. K.), Araldite CY178 (trade name; manufactured by Asahi-Ciba Ltd.), Chissonox 206 and Chissonox 205 (both trade names; manufactured by Chisso Corp.), and Celoxide 2021, Epolead GT301, Epolead GT302, Epolead GT401 and Epolead GT403 (all trade names; manufactured by Daicel Chemical Industries, Ltd.).
As the alicyclic epoxy compound, 3,4-epoxycyclohexylmethyl-3xe2x80x2,4xe2x80x2-epoxycyclohexanecarboxylate is particularly preferable.
The total amount of components A-2 is preferably in the range of 5 to 50 parts by weight relative to 100 parts by weight of the total amount of component A-1 and components A-2, and more preferably in the range of 10 to 40 parts by weight. When the total amount of components A-2, which are cross-linking components, is less than 5 parts by weight, the complex modulus of elasticity of the polymer obtained tends to be low, whereas the complex modulus of elasticity tends to become too high when the amount exceeds 50 parts by weight. There is as a result a high possibility that the complex modulus of elasticity might go outside the preferable range that is defined in the present invention.
The mixing proportion of the alicyclic epoxy compound used as component A-2 is not particularly limited as long as the complex modulus of elasticity of the polymer is in the preferable range. However, it is preferable for it to be added at 1 to 30 parts by weight relative to 100 parts by weight of the total amount of component A-1 and components A-2, and more preferably 2 to 20 parts by weight.
Cationic Polymerization Initiator (Component A-3)
The latent cationic polymerization initiator is a compound that can be activated by light or heat (hereinafter, called xe2x80x98photo-latentxe2x80x99 and xe2x80x98thermo-latentxe2x80x99 respectively) to generate an acid component and functions so as to induce the cationic ring-opening polymerization of a group capable of ring-opening polymerization in the composition.
With regard to a cationic polymerization initiator having photo-latent properties, any cationic photopolymerization initiator can be used as long as the polymerizable liquid composition of the present invention can be activated by irradiation with light, thereby inducing the ring opening of a group capable of ring-opening polymerization. Examples of the cationic photopolymerization initiator include onium salts and organometallic complexes. The light that can be used for the activation is preferably ultraviolet light. It is also possible to combine a photosensitizer with the initiator, thereby activating the composition of the present invention with short wavelength visible light having a wavelength of 390 to 500 nm.
Examples of the onium salt used as the photopolymerization initiator include diazonium salts, sulfonium salts and iodonium salts. Examples of the organometallic complex include an iron-allene complex, a titanocene complex and an allylsilanol-aluminum complex. It is also possible to use commercial products such as Optomer SP-150 (trade name; manufactured by Asahi Denka Kogyo K. K.), Optomer SP-170 (trade name; manufactured by Asahi Denka Kogyo K. K.), UVE-1014 (trade name; manufactured by General Electric Company), CD-1012 (trade name; manufactured by Sartomer Company, Inc.), and Rhodorsil 2074 (trade name; manufactured by Rhodia Inc.), which is (4-isopropylpheny)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate.
With regard to the cationic polymerization initiator having thermo-latent properties, any cationic thermopolymerization initiator can be used as long as it can be activated by heating and can induce the ring opening of a group capable of ring-opening polymerization. Examples thereof include various types of onium salt such as quaternary ammonium salts, phosphonium salts and sulfonium salts, and organometallic complexes. As the above-mentioned onium salts, for example, commercial products such as Adeka Opton CP-66 and Adeka Opton CP-77 (both trade names; manufactured by Asahi Denka Kogyo K. K.), San-aid SI-60L, San-aid SI-80L and San-aid SI-100L (all trade names; manufactured by Sanshin Chemical Industry Co., Ltd.) and the CI series (manufactured by Nippon Soda Co., Ltd.) can be used. Examples of the organometallic complexes include alkoxysilane-aluminum complexes.
The mixing ratio of the above-mentioned latent cationic polymerization initiator (A-3) is preferably in the range of 0.01 to 5 parts by weight relative to 100 parts by weight of the total amount of component A-1 and components A-2. When the mixing ratio of the latent cationic polymerization initiator is less than 0.01 parts by weight, there are cases where the ring-opening reaction of a group capable of ring-opening polymerization cannot be carried out sufficiently even by activation using the action of light or heat, and the tack properties of the polymer so obtained might be inadequate. When the initiator is added at more than 5 parts by weight, the effect of promoting the polymerization cannot be further enhanced, and the initial tack strength might even be degraded. Solid Resin (B)
The solid resin (B) is a tack-imparting resin (tackifier) that itself has a softening point of at least 40xc2x0 C., is compatible with the above-mentioned cationically polymerizable mixture (A) at room temperature, and is a component that adjusts the viscoelastic characteristics of the polymer. Adding the solid resin (B) to the cationically polymerizable mixture (A) can reduce the complex modulus of elasticity at low frequency (e.g., ca. 1 Hz) and can increase the complex modulus of elasticity at high frequency (e.g., ca. 100 Hz). A compound that is generally known as a tackifier can be used.
With regard to the solid resin (B), a solid resin that is generally know as a tackifier and has a comparatively low molecular weight and a high softening point can be used. For example, a tackifier such as a rosin resin, a modified rosin resin, a hydrogenated rosin resin, a terpene resin, a terpene phenol resin, an aromatic modified terpene resin, a C5 or C9 petroleum resin and a hydrogenated derivative thereof, or a chroman resin can be used. However, the solid resin (B) is not particularly limited by the above-mentioned resins as long as it is compatible with the aforementioned cationically polymerizable mixture (A) at room temperature and has a softening point of at least 40xc2x0 C.
Among the above-mentioned resins, a hydrogenated rosin resin and a hydrogenated petroleum resin are preferable in terms of their excellent compatibility with the cationically polymerizable mixture (A), improved transparency of the pressure-sensitive adhesive after curing, and their ability to exhibit a strong adhesive power.
The solid resin (B) is preferably used at 10 to 300 parts by weight relative to 100 parts by weight of the cationically polymerizable mixture (A), and particularly preferably 50 to 150 parts by weight. Other Optional Additives
(Compound Having Terminal Hydroxy Group)
The cationically polymerizable liquid composition of the present invention can contain a monool or polyol compound having a terminal hydroxy group.
Such a compound having a terminal hydroxy group is copolymerized into the polymer by a chain transfer reaction. When a compound having a hydroxy group at only one end of its straight chain is added, the cationic polymerization is terminated by the chain transfer reaction, and the hydroxy-containing compound is incorporated into the polymer chain. When a compound having hydroxy groups at both ends of its chain is added, since both terminal groups are incorporated into the polymer chain by chain transfer, it can function as a cross-linking chain. Adding a hydroxy-containing compound to the cationically polymerizable liquid composition in this way can adjust the viscosity of the composition and the viscoelasticity of the polymer after curing.
With regard to preferable hydroxy-containing compounds, diols and triols that are oligomers or polymers (hereinafter, simply called xe2x80x98polymersxe2x80x99) having a low glass transition temperature and a molecular weight in a specified range can be cited. The preferable range for the molecular weight is 300 to 10,000, more preferably 500 to 5,000, and particularly preferably 500 to 3,000. The atoms forming the main chain of the polymer are preferably carbon alone or carbon and oxygen. The number of atoms contained in the main chain connecting the two hydroxy groups is preferably 20 to 500, and more preferably 20 to 200.
The glass transition temperature of the above-mentioned polymer is preferably 0xc2x0 C. or below.
Preferred specific examples of the polymer containing a terminal hydroxy group include, as a compound having a hydroxy group at one end, the branched olefin polymer L-1203 manufactured by Kraton Polymers and, as compounds having hydroxy groups at both ends, the hydrogenated polybutadienes GI-1000, 2000 and 3000 manufactured by Nippon Soda Co., Ltd.
The composition of the present invention can contain, in addition to the above-mentioned cationically polymerizable mixture (A) and solid resin (B), a known plasticizer, anti-aging agent, filler, etc. as appropriate in amounts that do not interfere with the objects of the present invention. In order to enhance the coating performance, a viscosity increasing agent such as an acrylic rubber, an epichlorohydrin rubber, an isoprene rubber or a butyl rubber, a thixotropic agent such as colloidal silica or polyvinylpyrrolidone, a filler such as calcium carbonate, titanium oxide or clay, etc. can be added.
With the aim of imparting high adhesive shear strength, it is possible to add hollow inorganic materials such as glass balloons, alumina balloons or ceramic balloons; organic spheres such as nylon beads, acrylic beads or silicone beads; hollow organic materials such as vinylidene chloride balloons or acrylic balloons; and filaments such as glass, polyester, rayon, nylon or cellulose. When adding the above-mentioned glass filaments, although it is possible to add fibrous chips to the composition, carrying out the polymerization by impregnating a woven glass with the above-mentioned photopolymerizable composition, etc. can achieve very high adhesive shear strength.
Each of components A-1 to A-3 that form the cationically polymerizable mixture (A), solid resin B and the aforementioned other additives can be one type of compound; or two or more different types of compound can be combined.
The measurement conditions for the various physical properties that are used in the examples of the present invention and their preferable ranges are described below.
Viscosity
The viscosity of the cationically polymerizable liquid composition is 20 Paxc2x7sec or below at 25xc2x0 C. When the composition has a higher viscosity than the above-mentioned range, it becomes difficult to coat at room temperature and heating is required in some cases. Since heating a latent cationically polymerizable composition generally degrades its stability and increases the viscosity, heating is not desirable. In order to obtain good coating performance, the viscosity at 25xc2x0 C. is preferably 10 Paxc2x7sec or below.
Viscoelastic Characteristics
The complex modulus of elasticity of the polymer in the present invention is a value based on the result of a measurement obtained by a viscoelasticity measurement method using shear stress.
The complex modulus of elasticity (G*) of the cationic polymer obtained by cationic polymerization of the composition of the present invention preferably has viscoelastic characteristics at 25xc2x0 C. that satisfy the following conditions at each frequency.
G* greater than 100,000 (measurement frequency: 0.1 Hz)
G* less than 4,000,000 (measurement frequency: 1 Hz)
G* greater than 2,000,000 (measurement frequency: 100 Hz)
When a predetermined amount of an alicyclic epoxy compound is used as the aforementioned component A-2, the complex modulus of elasticity (G*) at a measurement frequency of 0.1 Hz at 100xc2x0 C. satisfies the following condition.
G* greater than 100,000 (measurement frequency: 0.1 Hz)
When the complex modulus of elasticity at 0.1 Hz of the polymer is less than 100,000, the cohesive strength of the polymer becomes undesirably low. When the polymer is peeled off from an adherend, cohesive failure takes place, thereby causing a so-called xe2x80x98glue residuexe2x80x99. An undesirable reduction in holding power might also occur in some cases. The complex modulus of elasticity at 0.1 Hz is more preferably 200,000 or above.
When the complex modulus of elasticity at 1 Hz is 4,000,000 or above, the polymer becomes hard and it undesirably shows no initial adhesion. It is more preferable for the complex modulus of elasticity at 1 Hz to be 3,000,000 or below.
When the complex modulus of elasticity at 100 Hz is less than 2,000,000, the tack value, which is essential for a pressure-sensitive adhesive, decreases. It is more preferable for the complex modulus of elasticity at 100 Hz to be 3,000,000 or above.
In order to obtain a high tack value it is preferable for the loss tangent (Tan xcex4) at 25xc2x0 C. to be at least 0.8 (measurement frequency: 100 Hz), and more preferably at least 1.0.
Glass Transition Temperature
The glass transition temperature (Tg) used in the present invention is a value based on the results measured by a DSC measurement method defined by JIS (Japanese Industrial Standards) K 7121.
When the glass transition temperature of a cationic polymer obtained by polymerizing the composition of the present invention exceeds 0xc2x0 C., it becomes difficult to maintain the above-mentioned viscoelastic characteristics, and it is therefore preferable for the glass transition temperature to be 0xc2x0 C. or below, and more preferably xe2x88x9220xc2x0 C. or below.
The polymerizable liquid composition of the present invention can be used for the production of a tacky polymer. When using the polymerizable liquid composition, for example, paper, plastic laminated paper, cloth, plastic laminated cloth, plastic film, metal foil, a foamed material, etc. is used as a support, the polymerizable liquid composition of the present invention is coated on one side or both sides of the support by an appropriate coating means such as a comma roll, a gravure coater, a roll coater, a kiss coater, a slot die coater, or a squeeze coater, the polymerization is effected by the application of heat or light, and a pressure-sensitive adhesive layer is formed so as to have a thickness of usually 10 to 500 xcexcm per side to give a pressure-sensitive adhesive sheet in tape form, sheet form, etc.
There is no particular limitation on the light source that can be used for carrying out polymerization by irradiation with light. Light sources having an emission energy distribution that extends to a wavelength of 400 nm or below can be used. Examples thereof include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a superhigh-pressure mercury lamp, a fluorescent lamp, a black light lamp, a microwave-excited mercury lamp and a metal halide lamp. The intensity of the light that irradiates the polymerizable liquid composition is controlled according to the target product and is not particularly limited, but it is preferable for the light intensity in the light wavelength region that is effective in activating the photo-latent initiator (depending on the photopolymerization initiator, but usually light at 300 to 420 nm) to be 0.1 to 100 mW/cm2. When the intensity of light that irradiates the polymerizable liquid composition is less than 0.1 mW/cm2, the reaction time becomes too long. When it exceeds 100 mW/cm2, there is a possibility that the heat radiated from the lamp and the heat generated during polymerization of the composition might reduce the cohesive strength of the pressure-sensitive adhesive layer so obtained, yellow the layer, and degrade the support.
The duration for which the light irradiates the polymerizable liquid composition is controlled according to the target product and is not particularly limited, but it is preferable to set the duration so that the accumulated amount of light represented by the product of the intensity and the duration of the irradiation with light in the above-mentioned light wavelength region is 10 to 5,000 mJ/cm2. When the accumulated amount of light that irradiates the above-mentioned polymerizable liquid composition is less than 10 mJ/cm2, active species cannot be generated sufficiently from the photo-latent initiator, thereby raising the possibility that the tack properties of the pressure-sensitive adhesive layer so obtained might be degraded. When it exceeds 5,000 mJ/cm2, the irradiation time becomes very long and it is disadvantageous in terms of productivity.
When polymerization is carried out using heat, the heat can be applied by a standard method to the cationically polymerizable liquid composition of the present invention, and the conditions therefor are not particularly limited.
The cationically polymerizable liquid composition of the present invention can, without containing a solvent, be coated easily on a substrate and can be used as a pressure-sensitive adhesive having good tack properties by the application of light or heat after coating. There is a high expectation that these novel pressure-sensitive adhesives that do not require an organic solvent to be removed will replace existing solvent type pressure-sensitive adhesives.